Tiktaalik roseae life restor

The Australian Outback is one of the most hostile environments on planet earth. Covering a land mass of nearly twenty two times the size of the United Kingdom, this dry landscape is a formidable and unforgiving adversary for the species that have adapted to inhabit it. But The Outback wasn’t always as dry as it is today. Millions of years ago, it was a lush, green biome that had rivers running in all directions. A recent archeological excavation has presented a team of scientists with a unique opportunity to name a fossil fish. Dr. Brian Choo of Findlers University and a team of researchers named the fish Harajicadectes zhumini after developing a more comprehensive understanding of the species. While fragments of Harajicadectes were discovered in 1973, a nearly complete specimen was unearthed by Flinders University in 2016, when they began constructing a comprehensive profile of the species.

By observing the skeletal remains, the team was able to reconstruct a hypothesized anatomy of the animal. One of its striking features was a series of large openings at the top of its head. “These spiracular structures are thought to facilitate surface air-breathing, with modern-day African bichir fish having similar structures for taking in air at the water’s surface,” commented Dr. Choo. In light of these findings, the team began to consider how the supplementary breathing apparatuses contribute to our evolutionary heritage. “The ability to supplement gill respiration with aerial oxygen likely afforded an adaptive advantage,” added Professor Long. Harajicadectes is a member of those intrepid water dwellers who brought life to land. Elpistostegalians gave way to limbed tetrapods in the evolutionary family tree.

The evolutionary edge that supplementary breathing gave Harajicadectes is not to be underestimated. It is widely understood that oxygen sustains life, but its immense significance can only be realized when looking at the molecular level of respiration. Mitochondria are one of the most ancient organelles and, according to the endosymbiont theory, preceded eukaryotic cells as aerobic bacteria. In the final and most powerful stage of Cellular respiration – oxidative phosphorylation – oxygen plays an essential role in ensuring that ATP is churning. Oxidative phosphorylation takes place in the mitochondrial inner membrane, where proton pumps transport hydrogen protons from the mitochondrial matrix to the intermembrane space where a gradient builds. Then, through simple diffusion, protons cross through the ATP synthase complex back into the matrix where they bind with O2 molecules, forming H2O as a byproduct. If Harajicadectes didn’t have access to oxygen on land, it would have only been able to leave the water for brief periods of time. This would have greatly reduced its competitive advantage on the shores and reduced the likelihood of limbed tetrapod evolution. 

I think the field of paleontology is an underappreciated field of biology and science. Just as the field of history provides context for the problems of today, paleontology better helps modern biologists understand how, when, and why species evolve as they do. This naming of the animal has been fifty years in the making, but thanks to the team of Australian scientists, we understand our evolutionary beginnings slightly better. I find the mapping of ancient biomes fascinating, and as more advanced chemistry develops, maybe one day scientists will be able to bring these prehistoric animals back to life. 



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